This invention relates to processes for manufacturing monolithic integrated circuits which include overlaid layers of dielectric materials. More specifically, this invention relates to a method for improved the adhesion between low-K dielectric material layers.
Dielectric material layers usually function to provide electric insulation between conductive layers and to protect underlying structures of the integrated circuit against contaminants (impurities, moisture) or impacts. The adjacency of dielectric material layers having the same or different compositions is a common occurrence in today""s technology at several manufacturing stages of integrated circuits. In such processes, a second layer is subsequently formed over a first layer of dielectric material. That second layer may overlap the first at a next stage so as to completely cover it, as is the case with certain passivating steps, for example. However, before forming the second layer, other operations are often carried out (such as the formation of a sacrificial layer which is then etched away, either fully or partially, or such as the partial removal of the first layer itself without using a sacrificial layer). In any case, the second dielectric layer will have bottom surface portions in direct contact with top surface portions of the first.
The provision of successive layers ensures protection for the device even when any one of the layers becomes damaged, e.g., by the formation of fine cracks. Therefore it is important that no regions be allowed to have less than perfect adhesion between the overlaid layers in the areas of contact. Nonetheless, some materials develop peculiar adhesion problems at the interface which are not fully understood by those skilled in the art.
These problems already exist on account of certain inherent properties of the materials. In fact, when these are placed in layer form over another material, they develop by inherent stresses a more or less marked tendency to deform the underlying structure into a more or less curved shape, which may be concave or convex, according to whether the stress is a tensile or a compressive one. Where the adjacent underlying structure is also formed of another layer of dielectric material, the magnitude of the force acting on the two layers may vary even when the stress is of the same type and perhaps of equal value, due to fact that the thicknesses are generally different. At high values of that stress, the layers tend to separate and possibly xe2x80x9cdelaminatexe2x80x9d. In general, spontaneous de-lamination occurs where the stress at the interface exceeds the molecular adhesion forces acting between the two layers. This problem is aggravated by the application of external mechanical loads which add further stress, e.g., while dicing the wafer on which the circuit is formed. Other significant influences may include changes in temperature during the circuit manufacturing cycle, and environmental chemical attacks; these effects are apt to degrade the interlayer bonds.
The difficulty of achieving adhesion of the layers is further enhanced by certain methods which are commonly applied during the manufacture of an integrated circuit.
In order to improve adhesion between dielectric materials, some techniques have been developed which provide treatments of the surface of an underlying layer prior to forming the next.
One prior solution consists of bombarding the surface of a layer to be deposited with ions of an inert gas, such as argon or nitrogen, under plasma (sputtering process). In this way, the roughness of the surface is enhanced mechanically to provide increased gripping area for the reactants to be deposited, which improves adhesion. That technique applies to the instance of oxide layers deposited using tetraethylorthosilicate as the precursor (known as TEOS).
Another solution disclosed by U.S. Pat. No. 5,795,821, it is provides an oxide adhesive agent between two dielectric material layers. In this way, it provides improved adhesion. However, particularly with dielectric material layers having low k (dielectric constant  less than 4), such as silicon carbide and SILK, they are ineffective to prevent separation of two successive layers.
It is an object of this invention to provide a method for improved the adhesion between dielectric material layers.
The other object of this invention is to provide a method to treat the surface of dielectric material layers with oxygen plasma to improve the adhesion thereof.
According to the above-mentioned objects, this invention provides a method to improve the adhesion between dielectric material layers at the interface thereof, during the manufacture of a semiconductor device. The first step is to form a first layer of dielectric material having a formula of SiCxNy, wherein xxe2x89xa70 yxe2x89xa70 and x+yxe2x89xa00. The oxygen ions are supplied into the first layer of dielectric material. A second layer of dielectric material is formed over the first layer of dielectric material.
The first layer of dielectric material used in this invention is selected from the group consisting of silicon carbide, silicon nitride and the mixture thereof. Preferably, this first layer is SiC-based dielectric material layer. The second layer is silicon based dielectric material, such as siloxane polymer low K film. Preferably, the second layer is LKD, which is an inorganic siloxane polymeric film.
Preferably, the step of supplying oxygen ion to the first layer of dielectric material is performed by oxygen plasma treatment.
The object of this invention also can be achieved by the steps as follows. A first layer of SiC-based dielectric material is formed on a substrate. The first layer of SiC-based dielectric material is treated by oxygen plasma. A second layer of silicon-based dielectric material is formed over the first layer of SiC-based dielectric material. A third layer of dielectric material, such as LKD, is formed over the second layer.